1. Field of the Invention
This invention relates to a method for reforming an undercoating surface prepared for the formation of a film by the CVD (chemical vapor deposition) technique using a reaction gas containing an ozone-containing gas having ozone (O.sub.3) contained in oxygen (O.sub.2) and tetraethylorthosilicate (TEOS) (hereinafter referred to as "O.sub.3 /TEOS reaction gas") and a method for the production of a semiconductor device.
2. Description of the Prior Art
The film formed by the CVD technique using the O.sub.3 /TEOS reaction gas (hereinafter referred to as "O.sub.3 /TEOS CVD SiO.sub.2 film") has the nature of exhibiting high density, a low etching rate, no shrinkage by a heat treatment even at high temperatures, a small water content, and fine flow quality prominently in accordance as the O.sub.3 concentration in O.sub.2 increases. The silicon oxide film formed by using an O.sub.3 /TEOS reaction gas containing O.sub.3 in a high concentration (hereinafter referred to as "high O.sub.3 /TEOS reaction gas") will be referred to as "high O.sub.3 /TEOS CVD SiO.sub.2 film" and the silicon oxide film formed by using an O.sub.3 /TEOS reaction gas containing O.sub.3 in a low concentration (hereinafter referred to as "low O.sub.3 /TEOS reaction gas") will be referred to as "low O.sub.3 /TEOS CVD SiO.sub.2 film" hereinafter.
The high O.sub.3 /TEOS CVD SiO.sub.2 film relies for its quality in a great measure on the condition of the surface of an undercoating layer. Particularly when a high O.sub.3 /TEOS CVD SiO.sub.2 film is formed on the surface of a SiO.sub.2 film or a Si.sub.3 N.sub.4 film, for example, the film undergoes abnormal growth and acquires a porous texture and a coarse surface as illustrated in FIG. 1 and suffers a decline in the growth rate of a film.
In contrast, when a low O.sub.3 /TEOS CVD SiO.sub.2 film is formed on the surface of an undercoating layer, such abnormal growth as is observed in the high O.sub.3 /TEOS CVD SiO.sub.2 film does not occur in this low O.sub.3 /TEOS CVD SiO.sub.2 film. The low O.sub.3 /TEOS CVD SiO.sub.2 film, however, is inferior in such film qualities as density to the high O.sub.3 /TEOS CVD SiO.sub.2 film.
For the purpose of forming a film of fine flow shape and high quality and conferring on the film an ability to be buried satisfactorily in a narrow depressed area, therefore, it is necessary to form the high O.sub.3 /TEOS CVD SiO.sub.2 film in such a manner as is not affected by the condition of the surface of an undercoating layer.
Heretofore, the following methods have been adopted for the purpose of depriving a high O.sub.3 /TEOS CVD SiO.sub.2 film prior to its formation of the dependency thereof on the surface of an undercoating film.
(1) A first method consists in exposing the surface of an undercoating layer 120 to plasma as illustrated in FIG. 2A. On the undercoating layer 120 which has been reformed consequently, a high O.sub.3 /TEOS CVD SiO.sub.2 film 121 is formed as illustrated in FIG. 2B.
(2) A second method consists in forming on an undercoating layer 130 a plasma SiO.sub.2 film 131 as an undercoating insulating film by the plasma CVD technique as illustrated in FIG. 3A. Thus, a high O.sub.3 /TEOS CVD SiO.sub.2 film 132 is formed on the undercoating insulating film 131 as illustrated in FIG. 3B.
The plasma SiO.sub.2 film 131 is enabled to acquire satisfactory adaptability for the high O.sub.3 /TEOS CVD SiO.sub.2 film 132 in terms of the formation of a film, depending on the condition of the film formation adopted by the plasma CVD technique during the formation of the plasma SiO.sub.2 film 131. When the plasma SiO.sub.2 film 131 of fine adaptability is formed as an undercoating insulating film on the surface of the undercoating layer 130 and then the high O.sub.3 /TEOS CVD SiO.sub.2 film 132 is formed on the plasma SiO.sub.2 film 131, therefore, the high O.sub.3 /TEOS CVD SiO.sub.2 film 132 consequently obtained acquires fine film qualities.
(3) A third method consists in forming on the surface of an undercoating layer 140 a low O.sub.3 /TEOS CVD SiO.sub.2 film 141 as an undercoating insulating film or forming an O.sub.3 /TEOS CVD SiO.sub.2 film under a low pressure (hereinafter referred to as "low pressure O.sub.3 /TEOS CVD SiO.sub.2 film") 141 as illustrated in FIG. 4A. A high O.sub.3 /TEOS CVD SiO.sub.2 film 142 is formed as illustrated in FIG. 4B on the undercoating insulating film 141. The high O.sub.3 /TEOS CVD SiO.sub.2 film 142 is easily formed because manifests fine adaptability for the low O.sub.3 /TEOS CVD SiO.sub.2 film or the low pressure O.sub.3 /TEOS CVD SiO.sub.2 film 141.
The conventional methods mentioned above, however, severally encounter the following problems.
(1) With the method which resorts to the exposure of the surface of the undercoating layer 120 to plasma, the success thereof in eliminating the dependency on the surface of the undercoating layer 120 is at the mercy of varieties of the surface of the unndercoating layer 120 and the condition of the emission of plasma. The condition of the plasma emission, therefore, cannot be common and standardized inclusively for all kinds of undercoating layer 120 but must be optimized with respect to the status of an individual undercoating layer 120.
(2) In the case of the method which forms the plasma SiO.sub.2 layer 131 as an undercoating insulating film, the plasma SiO.sub.2 film 131 has too inferior step coverage to suit application to such an undercoating layer as is furnished with fine and deep grooves.
(3) In the case of the method which forms the low O.sub.3 /TEOS CVD SiO.sub.2 film 141 or the low pressure O.sub.3 /TEOS CVD SiO.sub.2 film 141 as an undercoating insulating film in preparation for the formation of the high O.sub.3 /TEOS CVD SiO.sub.2 film 142, the low O.sub.3 /TEOS CVD SiO.sub.2 film 141 possesses an isotropic film-forming property and requires a thickness of not less than 100 nm for the purpose of averting the influence of the dependency on the surface of the undercoating layer. This film, therefore, is unfit for application to an undercoating layer which is furnished with fine and deep grooves, for example. The low O.sub.3 /TEOS CVD SiO.sub.2 film 141 is unfit for an undercoating insulating film because it has low density as compared with the high O.sub.3 /TEOS CVD SiO.sub.2 film.